Gesture is becoming an increasingly popular means of interacting with computers. However, it is still relatively costly
to deploy robust gesture recognition sensors in existing mobile platforms. We present SoundWave, a technique that leverages
the speaker and microphone already embedded in most commodity devices to sense in-air gestures around the device. To do this,
we generate an inaudible tone, which gets frequency-shifted when it reflects off moving objects like the hand. We measure
this shift with the microphone to infer various gestures. In this note, we describe the phenomena and detection algorithm,
demonstrate a variety of gestures, and present an informal evaluation on the robustness of this approach across different
devices and people.